Effect of high through-thickness compression on composite failure

As composite materials are now used in load conditions with increasing complexity and thickness, all the three-dimensional stress components become important and should be taken into account when predicting failures. In particular, the through-thickness stresses can play a crucial role in determining the in-plane behaviours and strength of a composite, laminate. The work presented in this PhD thesis aims to investigate failures due to complex stress fields at the root of a composite component in a dovetail assembly, where highly concentrated through-thickness stresses as well as in-plane tensile and interlaminar shear stresses are present. The problem was decoupled into two simpler multiaxial load cases which were studied separately: (1) through-thickness compression with interlaminar shear, and (2) through-thickness compression with longitudinal tension. They were investigated experimentally using new loading configuration in a biaxial test machine. This bridges the gap in reliable multiaxial experimental data which is lacking in the open literature. This was then combined with a finite element (FE) modelling approach to, develop simple failure criteria which are validated for engineering design purposes. A simple constitutive law which takes into account the effect of transverse compression and analytical tools which can be I easily utilised to predict stresses and failures in composites were also developed. The findings of this thesis were finally applied to a severely tapered dovetail composite specimen, together with some mitigation strategies, to predict its ultimate fibre failure load and the failure locations.